The throw-away rotating tool is a tool in which the throw-away tip that conducts cutting work is detachably attached to the body. There has been known a conventional throw-away rotating tool in which a cutting head (the throw-away tip) has a convex portion (convex connection) that is larger in diameter on a rear end side, and a tool shank (body) has a concave portion that is smaller in diameter on a leading end side as shown in JP 2002-501441 (see FIGS. 1 and 9, etc.)
The throw-away rotating tool disclosed in JP 2002-501441 is configured so that the throw-away tip is relatively rotated about the axial core until the throw-away tip contacts with a torque transmission wall formed in the body after the convex connection has been inserted into the concave portion in a state where phases of the body and the throw-away tip about the axial core are shifted from each other, to thereby connect the convex connection and the concave portion together by the aid of elastic deformation of the concave portion of the body. In the technique disclosed in JP 2002-501441, a travel of the throw-way tip in the axial direction is regulated by engagement of the convex connection and the concave portion. Also, a travel of the throw-away tip in a rotating direction of the body at the time of cutting is regulated by making the throw-away tip in contact with the torque transmission wall.
However, a travel of the throw-away tip in an opposite direction to the rotating direction of the body at the time of cutting is merely regulated by a frictional force developed between an outer peripheral surface of the convex connection of the throw-away tip and an inner peripheral surface of the concave portion of the body. When the inner peripheral surface of the concave portion is worn due to attachment/detachment of the throw-away tip or vibration during the cutting work, the frictional force is reduced so that the throw-away tip may come free from the body before the cutting edge of the throw-away tip reaches a tool lifetime. In that case, the body must be replaced with a fresh one ahead of the throw-away tip.
Under the circumstances, there has been disclosed a drill (throw-away rotating tool) that includes a cutting tip 2 (the throw-away tip) having a first longitudinal portion 15 (convex connection) projected on a rear end surface thereof, and a drill shaft 1 (body) having an accommodation concave portion in which the first longitudinal portion 15 (convex connection) is accommodated formed on a front end surface. The drill also includes a thread surface 16 projected on an outer peripheral surface of the first longitudinal portion 15 (convex connection), and an opposed surface 19 that is recessed in the inner peripheral surface of the accommodation concave portion 10, and engages with the thread surface 16 as shown in JP 2003-505261 (see FIGS. 3 and 4, etc.).
In the technique disclosed in JP 2003-505261, the first longitudinal portion 15 (convex connection) is fitted into the accommodation concave portion 10, and the cutting tip 2 (the throw-away tip) is screwed in a direction opposite to the rotating direction of the drill shaft 1 (body) to press up the thread surface 16 toward the opposed surface 19 while the rear end surface of the cutting tip 2 (the throw-away tip) is pressed against the front end surface of the drill shaft 1 (body) to fix the cutting tip 2 (the throw-away tip). The fixation is further reinforced during operation of the drill (throw-away rotating tool)